(1) Field of the Invention
This invention relates to a therapeutic agent for photodynamic therapy of the atherosclerosis of animals, especially of mammals. More particularly, the invention relates to specific fluorescent compounds having a tetrapyrrole skeletal structure. An effective quantity of the compound is administered to a host and light rays of necessary wavelength are applied to the area of atherosclerosis to be treated, thereby regressing the atherosclerotic lesion by the cytotoxic singlet oxygen produced by the compound which is photodynamically excited.
(2) Description of the Prior Art
Atherosclerosis is a general term for local diseases of arteries, in which the functions of arteries are depressed by the intimal thickening, hardening and reconstruction of arterial walls. Included in these diseases are coronary atherosclerosis inducing myocardial infarction and angina pectoris, atherosclerosis obliterating in peripheral artery and abdominal aorta, and cerebral atherosclerosis inducing transient cerebral ischemia and cerebral infarction. As referred to above, the atherosclerosis is quite a serious condition as a fatal disease inducing myocardial infarction, angina pectoris, cerebral apoplexy or the like.
At present, there are two approaches for treating the atherosclerosis. One of them is surgical treatment in which the portion affected by atherosclerosis is directly treated. The other measure is medical treatment in which etiological factors relating to the occurrence and aggravation of the symptom of atherosclerosis is remedied. The medical treatment is mainly adopted presently for preventing the worsening and the occurrence of terminal complication by total amelioration of undesirable factors with alimentotherapy, exercise cure and pharmacological treatment. Meanwhile, there are few potential agents and curative means for direct treatment of atherosclerosis.
In the ordinary diagnosis of atherosclerosis, morbid parts in respective internal organs are mainly detected. Meanwhile, there are few methods for the diagnosis of artery system, the early detection of atherosclerotic portion and their quantitative evaluation.
There is hitherto known a method of diagnosis and therapy of atherosclerosis by administering a hematoporphyrin derivative to hypercholesterolemia rabbits and applying light rays. A typical hematoporphyrin derivative is exemplified by Photofrin II, which is described in THE AMERICAN JOURNAL OF CARDIOLOGY, 56, pp 667-671, 1985 "Effect of Hematoporphyrin Derivative and Photodynamic Therapy on Atherosclerotic Rabbits".
However, it was clarified by experiments of the present inventors that, when Photofrin II is used, it cannot be caused to accumulated selectively in the atherosclerotic lesion and marked therapeutic effect cannot be expected.
Incidentally, the compounds themselves in the present invention are already known as photodynamic diagnostic and photodynamic therapeutic agents for cancer which are described in U.S. Pat. Nos. 4,693,885; 4,656,186; 4,675,338; and 4,977,177 and European Laid-Open Patent No. 210351. It should be noted, however, that the field of art in the present invention is of course different from the field of art in the diagnosis and the therapy of cancer.